This research project includes an investigation of the activation mechanism of the classical complement pathway initiator, Cl. Additionally, clinically useful methods will be developed for the quantitation of native Cl and free Cl subunits, and for the detection and quantitation of complement activation in human serum. Finally, physiological mechanisms of complement control will be investigated. Physicochemical and functional differences of precursor and activated Clq will be studied by techniques including differential sedimentation, circular dichroism spectroscopy, SDS polyacrylamide gel electrophoresis, isoelectric focusing, and hemolytic titration. Direct evidence for conformational changes in the Cl macromolecule with activation will be sought. Immunochemical techniques utilizing double diffusion and single radial diffusion will be developed to detect and quantitate Cl activation in human serum. Advantage will be taken of the difference in the Ouchterlony patterns of Cl and Cl. Additionally, antisera will be produced to neoantigens formed in Cl during activation and utilized to screen sera. The sera from patients with different immunological diseases will be tested by these techniques. Finally, the mechanisms of control of CL activation in human serum will be investigated. The role of Cl inactivator as well as any other possible serum regulators will be studied.